A sensory neuron may be characterized by a description of its receptive field. Such a description provides a model that serves to help in understanding the function of the neuron. The description of the receptive field also provides a basis for studying the anatomical nature of the neuron and its interconnection with other nerve cells. In this project, it is proposed to study aspects of the receptive fields of neurons in the vertebrate visual system. Physiological and anatomical techniques will be applied to the retina and the lateral geniculate nucleus. Three main groups of related experiments are proposed. Their ultimate goal is to provide further understanding of the causal relationships between anatomical structure and the physiologically determined function of individual neurons in the visual system. The first group of experiments involves simultaneous recording from neurons in the lateral geniculate nucleus and the retinal ganglion cells which provide input to them. The objective is to understand the way in which inputs to neurons of the lateral geniculate nucleus are organized, and the way in which these neurons interact. The second group of experiments entails correlating the receptive field size and properties of retinal ganglion cells with actual cell size and type. Certain receptive field properties that are closely related to anatomical structure will be characterized with electrophysiological techniques. Attempts will be made to identify specific ganglion cells which have been studied in this manner. Quantitative electron microscopic studies of vertebrate retinas make up the third major group of experiments. The aim is to relate synaptic connectivity of retinal neurons with their physiologically determined function.